A manhole comprises apparatus for providing an opening in a surface which opening is large enough to allow craftspersons to descend beneath the surface to obtain access to stored materials or equipment or underground installations. For example, manholes normally are located in roadways or streets to allow access to underground sanitary and storm sewers and utility conduits. These manholes include a metal frame supported by a brick or concrete base structure. The metal frame has an internal annular ledge for supporting a manhole cover which is level with the top of the frame and with a surrounding roadway surface. Because the manhole openings normally are in areas open to pedestrian and vehicular traffic, facilities for securely framing and covering the opening must be provided. Manholes also must be strong enough to withstand all external loadings such as, for example, the loading of vehicles which, invariably, will move across a top surface of the manhole.
In the prior art, a typical procedure has been to frame the opening with an iron casting. The casting includes a flanged surface that in supported on a structure which is disposed beneath the ground level. This supporting structure typically comprises concrete rings or bricks which are dimensioned so that a number of them are sufficient in height to allow a craftsperson to reach an underground installation, for example. The flanged surface of the manhole transmits the weight of the portions of the manhole, such as a cover, together with live surface loads, to the supporting structure.
The cast frame typically incorporates an inwardly projecting circumferential ledge. A cover is supported on the ledge and closes the manhole. The cover typically comprises a removable casting designed to carry the surface loads, and must transmit forces caused by those loads through the frame to the underground supporting structure. Desirably, the cover is heavy, and, preferably, it is bolted to other portions of the manhole in order to deter vandalism.
When resurfacing roadways, a layer of paving material is caused to become disposed over the existing pavement, resulting in the manhole cover being below the top surface of the new pavement and thereby causing a depression in the roadway. When another layer of surfacing material, for example, asphalt, is added to the surface of the roadway, it becomes necessary either to elevate the existing manhole frame to the new level of the roadway, or to install an extension which may be called an adapter between the frame and the cover. A common practice has been to elevate the existing manhole frame by removing the existing pavement around the manhole and increasing the height of support material beneath the manhole frame and then resupporting the frame on the top of the new support material. The level of the frame is adjusted by filling the space between the frame flange and the supporting structure with layers of bricks and mortar. The raised frame is then repositioned and the roadway area abutting the manhole is replaced.
This is a manual, time consuming procedure. Furthermore, should the relationship between the surface of the roadway and the frame be altered, either by settling of the roadway or by the addition of another surface layer, the structure must be dismantled and the brick and mortar courses be reformed. All adjustments such as those for height and slope angle must be made by attempting to fill the space under the frame flange with bricks and mortar. It should be clear that it is desirable to be able to adjust the frame position without disturbing the structure below grade.
An alternate method of changing the level of the frame and the cover includes the step of installing a riser ring or adapter at the top of the frame. The riser ring or adapter is of sufficient height to cause the manhole cover to be elevated to the new level of the roadway required to meet the new road surface. This method appears easy to perform but there are problems. First, with presently used adapters, severe loadings tend to move the adapter and cause the cover to rock because of uneven seating of the adapter with the frame. Thus, it can be difficult to line up the frame top exactly with the finished grade and to maintain alignment of parts of the manhole. Also, the installation of the above-described adapter for raising the elevation of the manhole cover is somewhat complicated and may require special tools.
There have been suggestions that an adjustable frame be used. In such a frame, portions may be raised by turning threaded portions. In this way, portions of the manhole can be raised, lowered or tilted in a variety of positions without riser rings or adapters. Examples of these schemes are indicated in U.S. Pat. Nos. 1,076,386, 2,930,295, 3,263,579, and 3,773,428. These kinds of arrangements feature the use of screw threads in which adjustments are performed from a top portion of the manhole.
The methods described above have not become very popular. There are a number of difficulties associated with them. For example, the adjusting screws often are concealed by an enlarged manhole cover. Cities and municipalities prefer the obvious economy of a standard, interchangeable cover. Secondly, manhole frames often include hollow sections for housing the screw mechanism. Inasmuch as these must be provided in the casting by cores, the cost is increased. Furthermore, locking devices are necessary because all the adjustments for these screw thread mechanisms are made from the top of the frame, that is adjustments are made from the surface of the roadway. The locking devices may be difficult to remove when further adjustments are required. This is because of the small size and the limited space available in typical designs. Because the screw mechanisms are positioned adjacent the surface of the roadway, plugging of the screw mechanism and abrasion by roadway materials may occur. Grease fittings have been used to avoid the abrasion and corrosion but that increases the expense of the assembly and, of course, introduces relatively small parts that can be lost in installation or omitted during the installation.
In another manhole, an adjustable manhole cover support comprises an outer ring having a circular internal opening. A plurality of threaded members are disposed about the interior of the circular opening. An insert is dimensioned to fit within the outer ring to a depth controlled by the abutment of the insert against threaded members and studs to engage and to extend through the threaded members to abut an undersurface of the insert to provide control of the depth of the insert into the outer ring and the angulation of the outer ring. The arrangement includes recesses in the external periphery of the outer ring and corresponding projections on the insert. Threaded inserts are positioned within each projection. Bolts desirably are provided in recesses below the insert so that the studs and their locking mechanisms do not interfere with access into the manhole.
This last described arrangement uses a pair of split rings and clamps which are positioned on top of an existing manhole metal frame so as to increase the effective elevation of the manhole cover and particularly the internal annular ledge which supports the manhole cover. Combinations of split rings and clamps provide a variety of height adjustments with the arrangement of the split rings forming a desirable annular configuration for receiving and holding the manhole cover at the desired increased height. The multiple rings are adjustable secured to the existing manhole metal frame and the roadway. Although the procedure can be performed in a relatively short time at low cost and addresses the problems heretofore associated with raising of the metal frames and the manhole cover supports thereby, the arrangement is somewhat complicated.
What is needed and what seemingly is not provided in the prior art is a manhole system which includes an adapter that is simplistic in its configuration and easy to install. Further, the sought after system should be such that multiple adapters may be used to elevate a manhole cover successively to each of a plurality of resurface elevations.